Melanogenesis is a process through which special melanin-producing cells, called melanocytes, produce melanin pigment. Melanocytes constitute 5% to 10% of cells in the basal layer of the epidermis. There are typically 1000 to 2000 melanocytes per square millimeter of skin. Although variable in size, melanocytes are typically seven micrometers in length.
Melanin levels vary across different human populations varying from lightly to darkly pigmented individuals, depending on the level of activity of melanocytes and the quantity of eumelanin and pheomelanin they produce. This process is regulated by the tyrosinase enzyme, which is required for melanocytes to produce melanin from the amino acid tyrosine, and is highly influenced by hormones, including the MSH and ACTH peptides that are produced from the precursor proopiomelanocortin. A low level of melanogenesis is stimulated by exposure to UV-B radiation.
Once synthesized, Melanin is stored in special structures called melanosomes. The melanosomes are shipped to the top layer of keratinocytes along arm-like structures called dendrites. Melanin plays an important role there in protection of skin from UV-induced damage. Individuals having low levels of endogenous pigmentation tend to have a high incidence of skin cancers and, hence, agents that induce melanogenesis hold potential as protective agents for UV-induced skin damage and carcinogenesis. Furthermore, chemical agents that induce pigmentation could also serve as differentiating agents for skin cancers. On the other hand, agents that induce depigmentation are valuable for treatment of moles, dark spots that appear on aging skin or specific skin conditions, such as keloids or post-inflammatory hyperpigmentation and skin whitening as desired in cosmetics. Melanogenesis is a complex process that remains incompletely understood. It warrants studies on the identification of cellular factors involved in this process and approaches for its safe and functional manipulation.
There is thus a need for an identification of target genes or proteins for regulating melanogenesis or pigmentation and for providing a screening method for compounds acting on melanogenesis or pigmentation.